Accumulation of phosphorylated α‐synuclein in dopaminergic neurons of transgenic mice that express human α‐synuclein

Parkinson's disease is neuropathologically characterized by the presence of Lewy bodies, whose major component is α-synuclein. We had previously generated transgenic mice that expressed human α-synuclein carrying an Ala53Thr point mutation (hα-syn140m) under the control of the rat tyrosine hydroxylase promoter and found that hα-syn140m was localized not only in the cytoplasm but also in the nuclei of mesencephalic dopaminergic neurons. In the present study, we carried out immunohistochemical analysis of the brain of Tg mice using anti-PSer129, an antibody that specifically recognizes α-synuclein phosphorylated at Ser129. The antibody detected only phosphorylated hα-syn140m, whereas phosphorylation of endogenous α-synuclein, if any, was below the detection limit of the method employed. The analysis showed that approximately one-third of the hα-syn140m-positive neurons in the midbrain of heterozygous Tg mice were concomitantly reactive to anti-PSer129. The ratio almost doubled in homozygotes, indicating that the phosphorylation level depends directly on the amount of substrate. In addition, the ratio did not change at least up to 48 weeks of age. These data strongly suggest that hα-syn140m underwent constitutive phosphorylation and that the phosphorylation level was maintained to a certain level until the aged stages. Remarkably, hα-syn140m localized in the nuclei seemed to be preferentially phosphorylated compared with that in the cytoplasm. Among kinases that have been reported to be involved in the phosphorylation of α-synuclein, the β subunit of casein kinase-2 was detected in the nuclei by immunohistochemistry. These data imply that at least casein kinase-2 is involved in the phosphorylation of hα-syn140m in the Tg mice. © 2007 Wiley-Liss, Inc.